Deposition systems and methods are commonly used to form layers such as relatively thin films on substrates. For example, a chemical vapor deposition (CVD) reactor system and process may be used to form a layer of semiconductor material such as silicon carbide (SiC) on a substrate. CVD processes may be particularly effective for forming layers with controlled properties, thicknesses, and/or arrangements such as epitaxial layers. Typically, in a deposition system, such as a CVD system, the substrate is placed in a chamber and a process gas including reagents or reactants to be deposited on the substrate is introduced into the chamber adjacent the substrate. The process gas may be flowed through the reaction chamber in order to provide a uniform or controlled concentration of the reagents or reactants to the substrate. Undesirably, the reagents or reactants may tend to deposit on interior surfaces of the reaction chamber as well. Such deposits may be referred to as “parasitic” deposits because they remove reagents or reactants from the process.
With reference to FIG. 5, an exemplary conventional deposition system 40 is shown therein and illustrates the process by which deposits may be formed on unintended surfaces of a reaction chamber. The system 40 is, for example, a flow through, hot wall, CVD reactor. The system 40 has a top susceptor member 42 and a bottom susceptor member 44. The system 40 also has a top liner 43 and a bottom liner 45 defining a reaction chamber 47 therebetween. A substrate 20, such as a wafer, is positioned in the reaction chamber 47 and may be situated on an interior surface of a platter (which may rotate), for example. A process gas is introduced to the reaction chamber 47 at one end, flowed through the reaction chamber 47 past the substrate 20, and finally exhausted from the reaction chamber 47 at the opposite end. As indicated by the arrows in the reaction chamber 47 as shown in FIG. 5, as the process gas flows through the reaction chamber 47 a portion of the process gas may contact the substrate 20 as intended and thereby deposit the reagents or reactants on the substrate 20 to form a layer thereon. However, as indicated by the arrows, a portion of the process gas also contacts an interior surface or ceiling 46 of the top liner 43 as well as interior surfaces of the bottom liner 45 and side walls. As a result, parasitic deposits 50 and 52 of the reagents or reactants from the process gas tend to form on the ceiling 46 and the bottom liner 45, respectively, as well as on the sidewalls. The parasitic deposits on the ceiling 46 may be particularly harmful because they may dislodge and fall onto the substrate 20 during processing, reducing the quality of the formed layer. Moreover, the changing amount of the parasitic deposits may introduce undesirable variations in temperature and gas flow dynamics, thereby influencing the growth of the layer on the substrate 20. Depletion of the process gas because of the formation of the parasitic deposits may tend to waste reactants, thereby reducing efficiency and growth rate.
Typically, the deposition process is managed to accommodate the formation of parasitic deposits. The cumulative growth time may be limited to reduce the impact of parasitic deposits on product material. After a set time, the susceptor may be cleaned and reconditioned before more production growth runs are attempted. This procedure may limit both the possible length of any single growth run and the number of runs of shorter duration between cleaning cycles. Despite such efforts, parasitic deposits may nonetheless negatively impact product material due to particle formation, process variability and reduced reactant utilization efficiency.